Heating plate welding machine with mobile table

ABSTRACT

The welding machine comprises within a frame ( 1 ), a horizontal heating plate ( 21 ), a first lower piece-holder ( 22 ), a second upper piece-holder ( 23 ), means ( 41 ) for displacing horizontally the heating plate ( 21 ), means ( 42 ) for displacing vertically ( 29 ) the heating plate ( 21 ), and means ( 26 ) for displacing vertically the second piece-holder ( 23 ). The heating plate ( 21 ) and its vertically actuating cylinder ( 42 ) constitute an assembly connected to a heating plate carrier ( 33 ) by indexing means ( 27 ) for adjusting the vertical position of the vertical displacement ( 29 ) of the heating plate ( 21 ). The first piece-holder ( 22 ) is a telescoping table with adjustable height and capable of being locked mounted on the frame ( 1 ). Thus the possibilities of adjusting and adapting the welding machine to the different sizes of pieces to be welded are increased.

SUMMARY OF THE INVENTION

The present invention concerns heating plate welding machines, which aregenerally used to weld together two heat-weldable material parts alongrespective plane or non-plane connecting surfaces.

In the heating plate welding machines usually employed, such as thatdescribed in document FR 2 320 839 A, for example, a frame carries thevarious functional units of the machine including a heating plate, afirst workpiece support device, and a second workpiece support devicefacing the first workpiece support device. First means move the heatingplate along a transverse insertion travel parallel to its plane betweena welding position engaged between the first and second workpiecesupport devices and a loading position withdrawn from the first andsecond workpiece support devices. Second means move the heating platealong a welding travel perpendicular to its plane between two extremepositions. The first workpiece support device is fixed to the frame. Thesecond workpiece support device is mobile, and can be moved by thirdmeans along a contact travel perpendicular to the plane of the heatingplate between the extreme positions and toward or away from the firstworkpiece support device. The machine also includes cylinders for movingthe first workpiece support device toward or away from the secondworkpiece support device.

The movements of the heating plate, along the insertion travel and alongthe welding travel, are generally linear and driven by cylinders whichprovide amplitudes of movement limited by the allowed overall size ofthe cylinders of the machine. Similarly, the second workpiece supportdevice is moved along the contact travel by a cylinder providing alimited amplitude of movement.

In operation, at least one first workpiece to be welded is placed on thefirst workpiece support, while at least one second workpiece to bewelded is fixed to the second workpiece support, dedicated toolingproviding the connection between each workpiece support and thecorresponding workpiece to be welded. The machine is set up so thatduring a heating step the first face of the heating plate can be pressedonto the first workpiece to be welded on the first workpiece support,while the second workpiece to be welded is pressed against the oppositeface of the heating plate by the second workpiece support. The secondworkpiece support is then moved away, after which the heating plate ismoved away from the first workpiece to be welded carried by the firstworkpiece support and then withdrawn from the two workpiece supports.The second workpiece support is operated again to press the connectingsurfaces of the two workpieces to be welded against each other, theplastics material being sufficiently softened or melted to assure aweld.

Clearly, for each given machine, the various movements that arenecessary limit the maximal dimensions of workpieces that can be welded.

Workpieces of different shapes can be welded on the same machine byfitting appropriate dedicated tooling, but setting up the machine iscomplex because the travels of the cylinders moving the heating plateand the second workpiece support device are affected by the differencesin the dimensions of the tooling and the workpieces to be welded.

Accordingly, in document FR 2 320 839 A, the adjustment can be effectedby the cylinders moving the first workpiece support. This kind ofadjustment is not reliable, however, and no adjustment means areexplicitly described, and also this document concerns the welding ofstorage battery housings, the dimensions of which would appear to beconstant.

Document FR 2 688 736 A describes a similar machine, but in which thefirst workpiece support is fixed, without any adjustment means.

Document GB 2 085 354 A (FIG. 5) describes a similar machine in whichthe heating plate is suspended vertically from a carriage that ismovable to adjust it, and so is not positively held so that it can bemoved along a particular welding travel. This means that the weld is notreproducible.

Accordingly, in prior art machines, there are no means for reliably andquickly adjusting the machine to track variations in the size of theworkpieces to be welded, and to maintain the pressures exerted duringoperation of the machine effectively.

SUMMARY OF THE INVENTION

The problem addressed by the present invention is that of designingimprovements to machines for welding workpieces using heating plateswhich, without modifying the overall size of the machine, and usingconventional tooling available until now, significantly increase thepossible variation in the dimensions of the workpieces that the machinecan weld, retaining good reproducibility of the weld.

The improved possibilities of modifying the dimensions of workpieces tobe welded must preferably be obtained without complicating theoperations of control of the cylinders actuating the mobile parts of themachine, and without increasing the travel itself of the cylinders, sopreserving a good speed of the welding cycle.

Accordingly, an improved machine in accordance with the invention mustbe able to replace a plurality of existing machines each suited to arange of dimensions of the workpieces to be welded.

To achieve the above and other objects, a welding machine in accordancewith the invention having a heating plate comprises a frame, a heatingplate, a first workpiece support device, a second workpiece supportdevice facing the first workpiece support device, first means for movingthe heating plate along an insertion travel parallel to its planebetween a welding position engaged between the first and secondworkpiece support devices and a loading position withdrawn from thefirst and second workpiece support devices, second means for moving theheating plate along a welding travel perpendicular to its plane betweentwo extreme positions, and third means for moving the second workpiecesupport device along a contact travel perpendicular to the plane of theheating plate toward and away from the first workpiece support deviceand between respective bearing and withdrawn positions, together withmeans for moving the first workpiece support device perpendicular to theheating plate toward or away from the second workpiece support device.

The first workpiece support device further comprises:

an adjustable position table, mounted on the frame, being movable ittoward or away from the second workpiece support device, and

means for locking the table in a particular position chosen from a setof predefined positions and to withstand thus pressure forces exerted onthe table during operation of the machine.

This means that the workpiece supports and the heating plate aremechanically strong, to guarantee good reproducibility of the weld.

For example, the means for locking the table comprise transverse screwsselectively engaged in corresponding holes in respective fixed lateralguide plates of the frame and in guide brackets carried by the table.

Improved possibilities of adjusting the machine can be obtained byfurther providing indexing means for indexing the welding travel of theheating plate by moving its two extreme positions of welding travelperpendicularly to the plane of the heating plate toward or away fromthe first workpiece support device.

In one advantageous embodiment, the table comprises a top plate joinedto a bottom support by expandable connecting members each including afirst arm, one end of which is articulated to the bottom support and theother end of which slides under the top plate, and a second arm, one endof which is articulated under the top plate and the other end of whichslides on the bottom support, the two arms being articulated to eachother in their central areas, the sliding end of the second arm beingslid horizontally on the bottom support by a cylinder to adjust theheight of the table.

The design of a machine of the above kind can be adapted to heatingplates oriented vertically or horizontally. In a preferred embodiment,the heating plate is oriented in a substantially horizontal position,its insertion travel is substantially horizontal and its welding travelis substantially vertical, the first workpiece support device is in alower position on the frame, and the second workpiece support device isin an upper position on the frame and its contact travel issubstantially vertical.

The means for indexing the welding travel of the heating plate canadvantageously be such that:

the heating plate support carriage comprises at least two verticallateral flanges each having an indexing opening with a vertical linearmain part, one end of which is joined to a plurality of obliquesecondary parts diverging from each other in the downward direction andoffset from each other in the vertical direction,

the heating plate support frame comprises transverse horizontal lugs orrods engaging in the indexing openings of the heating plate supportcarriage, and able to slide in said indexing openings to penetrateselectively into one of the oblique secondary parts and to abut againstits bottom.

An advantageous arrangement for reducing the overall size of the weldingmachine is for the heating plate support carriage to be moved, along itsinsertion travel, by two horizontal cylinders in the upper part of theframe on respective opposite sides of the interior part of the frame.

With a machine of the above kind with improved adjustment possibilities,it is advantageous for the door providing access to the interior spaceof the frame to open quickly and wide. To this end, the door maycomprise two telescopic lateral flaps.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willemerge from the following description of specific embodiments, givenwith reference to the accompanying drawings, in which:

FIG. 1 is a side view of a heating plate welding machine constitutingone embodiment of the invention, showing the heating plate in theloading position and the lateral wall of the frame removed;

FIG. 2 is a plan view of the welding machine from FIG. 1 showing thedoor open, the heating plate in the loading position and the top wallremoved;

FIG. 3 is a front view of the welding machine from FIG. 1 showing thedoor open;

FIG. 4 is a partial side view in section, showing the means for indexingthe heating plate support in one embodiment of the present invention;

FIG. 5 is a side view showing in detail the construction of a variableheight table in one embodiment of the present invention; and

FIG. 6 shows the possibilities of adjusting the welding machine fromFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the embodiment shown in the figures, in particular in FIGS. 1 to 3, awelding machine in accordance with the invention comprises asubstantially parallelepiped-shape frame 1 defining an interior space 2containing all of the functional units of the welding machine. The frame1 comprises a supporting structure defined overall by four verticaluprights 3, 4, 5 and 6 disposed at the four corners of the interiorspace 2, two bottom longitudinal members 7 and 8, two end bottomcrossmembers 9 and 10, and two opposed top longitudinal members 11 and12 and two end top crossmembers 13 and 14.

In the embodiment shown, there are also two opposed intermediatelongitudinal members 15 and 16, substantially three-quarters the heightup the frame 1, together with intermediate uprights 17 and 18 near theuprights 4 and 5, respectively.

An electrical equipment cabinet 19, containing switching and controldevices, is provided against the rear face of the frame defined by therear uprights 3 and 6 and the rear crossmembers 9 and 13. A door system20 is provided against the front face of the frame defined by the frontuprights 4 and 5 and the front crossmembers 10 and 14.

The interior space 2 of the frame 1 contains the functional units of thewelding machine, including particularly a heating plate 21, a firstworkpiece support device 22, a second workpiece support device 23 facingthe first workpiece support device 22, first means 24 for moving theheating plate 21 along an insertion travel 39 parallel to its plane,second means 25 for moving the heating plate 21 along a welding travel29 perpendicular to its plane, and third means 26 for moving the secondworkpiece support device 23 along a contact travel 129 perpendicular tothe plane of the heating plate 21. In accordance with the invention,indexing means 27 are further provided for indexing the welding travel29 of the heating plate 21, by movement of its two extreme positionsperpendicularly to the plane of the heating plate 21 toward or away fromthe first workpiece support device 22.

In the embodiment shown in the figures, the heating plate 21 issubstantially horizontally oriented, its insertion travel 39 issubstantially horizontal and its welding travel 29 is substantiallyvertical. The first workpiece support device 22 is in the bottom part ofthe interior space 2 on the frame 1 and the second workpiece supportdevice 23 is in the top part of the interior space 2 of the frame 1, itscontact travel 129 being substantially vertical.

The heating plate 21 is mounted on a mobile heating plate supportbracket 28 in turn movable in vertical translation along said weldingtravel shown by the arrow 29 in FIGS. 1 and 4, perpendicularly to theplane of the heating plate 21, sliding on vertical guides 30 and 31 of aframe 32 in turn carried by a heating plate support carriage 33.

The heating plate support carriage 33 has a carriage top maincrossmember 34 the ends of which have skids 35 and 36 which slide onlongitudinal guides carried by the intermediate longitudinal members 15and 16. The heating plate support carriage 33 also has two vertical sideflanges 37 and 38 shaped to retain the frame 32 and joined at their topends by a horizontal connecting plate 133 retained by the top maincrossmember 34. The horizontal connecting plate 133 is preferablymounted to slide longitudinally in the direction of the welding travel29, its two lateral edges being engaged in lateral slides 134 and 135fastened to the top main crossmember 34. A rear adjuster screw 136adjusts the longitudinal position of the flanges 37 and 38 and of theconnecting plate 133 relative to the top main crossmember 34, soallowing fine adjustment of the position of the heating plate for thewelding step, as shown by the arrow 139.

In executing its insertion longitudinal travel 39 shown in FIG. 1, theheating plate support carriage 33 slides on the longitudinal guides whenacted on two horizontal cylinders 40 and 41 in the top part of the frame1 on respective opposite sides of the interior welding space 2 andcoupled to the ends of the top main crossmember 34.

The particular position of the cylinders 40 and 41 actuating the heatingplate 21 along the insertion travel 39 produces a compact weldingmachine that is short in length.

In executing its welding travel 29, the mobile heating plate supportbracket 28 slides on the vertical guides 30 and 31 of the frame 32 andis operated on by a vertical cylinder 42 carried by the frame 32 and thetravel of which is adjustable.

In accordance with the invention, the position of the first workpiecesupport device 22 can be adjusted by movement perpendicular to theheating plate 21, in the vertical direction, toward or away from thesecond workpiece support device 23.

To this end, in the embodiment shown in FIGS. 1 and 5, the firstworkpiece support device 22 can include an adjustable height table 50mounted on the frame 1, for example.

In the embodiment shown, the table 50 has a top plate 51 connected to afixed bottom support 52 by expandable connecting members each including:a first arm 53, one end 54 of which is articulated to the bottom support52 and the other end 55 of which slides under the top plate 51, and asecond arm 56, one end 57 of which is articulated under the top plate 51and the other end 58 of which slides on the bottom support 52. The twoarms 53 and 56 are articulated to each other in their central areas 59,and the sliding end 58 of the second arm 56 is slid horizontally on thebottom support 52 by a cylinder 60 to adjust the height of the table 50.

As shown in FIG. 3, the table 50 can be immobilized or locked in aparticular position chosen from a set of predefined vertical positionsby transverse screws such as the screws 150 and 151 selectively engagedin corresponding holes respectively formed in fixed lateral guide plates152 and 153 of the frame 1 and in guide brackets 154 and 155 carried bythe table 50.

The operation of the welding machine is described hereinafter. In theloading position, shown in FIGS. 1 to 3, the heating plate 21, carryingheating blocks with the same profiles as the respective connectingsurfaces of the workpieces to be welded, is in a loading position,withdrawn from the first and second support devices 22 and 23, thesecond workpiece support device 23 being withdrawn from the firstworkpiece support device 22. A first workpiece to be welded, held on thefirst workpiece support device 22 by a first dedicated tooling adaptedto the shape of the first workpiece to be welded and shaped to be fixedto the first workpiece support device 22, can then be moved into place.The second workpiece to be welded, fixed to the second workpiece supportdevice 23 by second dedicated tooling adapted to the shape of the secondworkpiece to be welded and shaped to be fixed to the second workpiecesupport device 23, can equally be moved into place. The respectiveconnecting surfaces of the two workpieces to be welded are thenface-to-face and separated from each other.

The cylinders 40 and 41 move the heating plate 21 along the insertiontravel 39 between the two workpieces to be welded, that is to saybetween the first and second workpiece support devices 22 and 23, in thesufficient gap that must exist between the two connecting faces of theworkpieces to be welded. The cylinder 42 lowers the heating plate 21along the welding travel 29 until the bottom face of its lower heatingblock is pressed against the connecting face of the first workpiece tobe welded fixed to the first workpiece support device 22, the heatingplate 21 then bearing against abutments carried by the tooling of thefirst workpiece support device 22. The cylinder 26 lowers the secondworkpiece support device 23 along the contact travel 129 so that theconnecting face of the second workpiece to be welded that it carries ispressed against the top face of the top heating block of the heatingplate 21, abutments carried by the tooling of the second workpiecesupport device 23 bearing against the heating plate 21. The heatingplate 21, which is maintained at an appropriate temperature byelectrical heating elements connected to an external electrical powersupply, heats the two connecting faces of the workpieces to be weldedand partially melts their surfaces.

The cylinder 26 then raises the second workpiece support 23 after whichthe successive operation of the cylinder 42 and of the pair of cylinders40 and 41 raises the heating plate 21 and then moves it to the loadingposition withdrawn from the first and second workpiece support devices22 and 23, after which the cylinder 26 lowers back the second workpiecesupport device 23 until the two connecting faces of the workpieces to bewelded are pressed together. The two workpieces to be welded are pressedtogether for long enough to effect the weld, and finally the secondworkpiece support device 23 is raised and the two workpieces that havebeen welded together are removed.

The invention enables the position of the first workpiece support device22 to be adapted to the respective size of the two workpieces to bewelded reliably, quickly and at low cost. To this end, depending on theworkpieces to be welded, the first workpiece support device 22 ispositioned at an appropriate vertical position, by actuating thecylinder 60. Movement of the first workpiece support device 22 isthereafter prevented by inserting the transverse screws 150 and 151 inthe corresponding holes in the plates 152 and 153 and the brackets 154and 155.

Accordingly, without increasing the welding travel 29 of the heatingplate 21, the total relative vertical area that the heating plate 21 canreach is increased in size, which increases the range of different sizesof workpieces that can be welded.

FIG. 6 shows this first possibility of adaptation in accordance with theinvention. The righthand part of the figure shows several possiblepositions of the first workpiece support device 22, to which it is movedby the cylinder 60. Clearly the bottom position is suitable when thefirst workpiece to be welded is high and the second workpiece to bewelded is relatively low. Conversely, the upper position is suitablewhen the first workpiece to be welded has a lower height and the secondworkpiece to be welded has a greater relative height.

The combination of the frame 32, the heating plate support bracket 28and the cylinder 42 can additionally or instead be moved vertically inits entirety by the indexing means 27 to execute an indexing movementbetween a plurality of distinct positions on the heating plate supportcarriage 33. This indexing movement simultaneously moves both extremepositions of the welding travel 29 of the heating plate 21. In this waythe position of the extreme positions of the welding travel 29 can bechosen in the interior space 2, allowing adaptation to the size of theworkpieces to be welded.

In the embodiment shown in the figures, and in particular in FIG. 4, theindexing means 27 for indexing the welding travel 29 of the heatingplate 21 comprise means for selectively fixing the frame 32 to theheating plate support carriage 33 in a plurality of positions offsetfrom each other in the vertical direction perpendicular to the heatingplate 21.

In practice, the heating plate support carriage 33 comprises at leasttwo vertical side flanges 37 and 38 each of which has an indexingopening such as the opening 42. The opening 42 has a vertical linearmain part 43, a vertical edge 44 of which is joined to a plurality ofoblique secondary parts 45, 46, 47 and 48 diverging in the downwarddirection, offset from each other in the vertical direction, as shown,and having bottoms aligned with a common vertical axis.

The frame 32 has horizontal lugs or rods 49, oriented transversely andshaped to engage in the indexing openings such as the opening 42 of theheating plate support carriage 33 and to slide in said indexing openings42 to penetrate selectively into one of the oblique secondary parts 45through 48 and to abut against the bottom of said chosen obliquesecondary part 45 to 48. Corresponding faces of the heating platesupport carriage 33 and of the frame 32 form bearing surfaces opposingtilting of the armature, for holding the heating plate 21 in a fixedhorizontal position relative to the heating plate support carriage 33.

The lefthand part of FIG. 6 shows the additional possibilities ofvertical adjustment provided by the indexing means 27. Clearly thewelding travel 29 can be moved vertically and the possibilities ofadapting the position of the heating plate 21 relative to the firstworkpiece support device 22 according to the sizes of the workpieces tobe welded can be increased.

The additional possibilities for adjusting the relative heightwisepositions of the functional units of the welding machine lead to theprovision of a door system 20 that is well adapted to suchpossibilities. A door with two telescopic lateral flaps that retractlaterally is preferably employed, as shown in FIG. 2: the door, which isshown in the open position in the figure, has a first telescopic lateralflap formed of a first panel 61 and a second panel 62 sliding laterallyrelative to each other and relative to the frame 1. Similarly, atelescopic second lateral flap comprises a first panel 63 and a secondpanel 64 sliding laterally relative to each other and relative to theframe 1. This provides a door that is of compact overall size in theopen position, and that can be closed and opened very quickly during theoperating cycle.

The present invention is not limited to the embodiments explicitlydescribed, but includes variants and generalizations thereof within thescope of the following claims.

What is claimed is:
 1. Welding machine having a heating plate (21),comprising a frame (1), a heating plate (21), a first workpiece supportdevice (22), a second workpiece support device (23) facing the firstworkpiece support device (22), first means (24) for moving the heatingplate (21) along an insertion travel (39) parallel to its plane betweena welding position engaged between the first and second workpiecesupport devices (22, 23) and a loading position withdrawn from the firstand second workpiece support devices (22, 23), second means (25) formoving the heating plate (21) along a welding travel (29) perpendicularto its plane between two extreme positions, and third means (26),different from the second means (25), for moving the second workpiecesupport device (23) along a contact travel (129) perpendicular to theplane of the heating plate (21) toward and away from the first workpiecesupport device (22) and between two respective bearing and withdrawnpositions, together with means for moving the first workpiece supportdevice (22) perpendicular to the heating plate (21) toward or away fromthe second workpiece support device (23), the first workpiece supportdevice (22) further comprising: an adjustable position table (50)mounted on the frame (1), the table (50) being movable toward or awayfrom the second workpiece support device (23), and means (150-155) forlocking the table (50) in a particular position chosen from a set ofpredefined positions and to withstand pressure forces exerted on thetable (50) during operation of the machine.
 2. A welding machine asclaimed in claim 1, wherein the means (150-155) for locking the table(50) comprise transverse screws (150, 151) selectively engaged incorresponding holes in respective lateral guide plates (152, 153) fixedto the frame (1) and in guide brackets (154, 155) carried by the table(50).
 3. A welding machine as claimed in claim 1 further comprisingindexing means (27) for indexing the welding travel (29) of the heatingplate (21) by movement of its two extreme positions of welding travel(29) perpendicular to the plane of the heating plate (21) toward or awayfrom the first workpiece support device (22).
 4. A welding machine asclaimed in claim 3, wherein the table (50) comprises a top plate (51)joined to a bottom support (52) by expandable connecting members eachincluding a first arm (53), one end (54) of which is articulated to thebottom support (52) and the other end (55) of which slides under the topplate (51), and a second arm (56), one end (57) of which is articulatedunder the top plate (51) and the other end (58) of which slides on thebottom support (52), the two arms (53, 56) being articulated to eachother in their central areas (59), the sliding end (58) of the secondarm (56) being slid horizontally on the bottom support (52) by acylinder (60) to adjust the height of the table (50).
 5. A weldingmachine as claimed in claim 1, wherein the heating plate (21) is mountedon a mobile heating plate support bracket (28) movable in translationalong said welding travel (29) perpendicular to the plane of the heatingplate (21) on a frame (32) itself carried by a heating plate supportcarriage (33), the heating plate support carriage (33) being itselfmovable along said insertion travel (39) parallel to the plane of theheating plate (21) on first guides (15, 16) attached to the frame (1),indexing means (27) for indexing the welding travel (29) of the heatingplate (21) comprising means for selectively fixing the heating platesupport frame (32) on the heating plate support carriage (33) in aplurality of positions offset from each other in the directionperpendicular to the heating plate (21).
 6. A welding machine accordingto claim 5 wherein the heating plate (21) is oriented in a substantiallyhorizontal position, its insertion travel (39) is substantiallyhorizontal and its welding travel (29) is substantially vertical, thefirst workpiece support device (22) is in a lower position on the frame(1) and the second workpiece support device (23) is in an upper positionon the frame (1) and its contact travel (129) is substantially vertical.7. A welding machine as claimed in claim 6 wherein: the heating platesupport carriage (33) comprises at least two vertical lateral flanges(37, 38) each having an indexing opening (42) with a vertical linearmain part (43), one end (44) of which is joined to a plurality ofoblique secondary parts (45-48) diverging from each other in thedownward direction and offset from each other in the vertical direction,the heating plate support frame (32) comprises transverse horizontallugs or rods (49) engaging in the indexing openings (42) of the heatingplate support carriage (33), and able to slide in said indexing openings(42) to penetrate selectively into one of the oblique secondary parts(45-48) and to abut against its bottom.
 8. A welding machine as claimedin claim 6, wherein the heating plate support carriage (33) is movedalong its insertion travel by two horizontal cylinders (40, 41) in theupper part of the frame (1) on respective opposite sides of the interiorpart (2) of the frame (1).
 9. A welding machine as claimed in claim 5,wherein the mobile heating plate support bracket (28) slides on guides(30, 31) of the frame (32) and is moved along its welding travel (29) bya cylinder (42) carried by the frame (32).
 10. A welding machine asclaimed in claim 1, wherein the frame (1) comprises a door (20) with twotelescopic lateral flaps (61, 62; 63, 64).
 11. A welding machine asclaimed in claim 1, wherein: in the extreme position of the weldingtravel of the heating plate (21) in which the first heating block ispressed against the connecting face of the first workpiece to be weldedfixed to the first workpiece support device (22), the heating plate (21)is in bearing engagement with abutments carried by the tooling of thefirst workpiece support device (22), and in the bearing engagementposition of the second workpiece support device (23), in which theconnecting face of the second workpiece to be welded is pressed againstthe top face of the second heating block of the heating plate (21),abutments carried by the tool of the second workpiece support device(23) are in bearing engagement with the heating plate (21).